Extremity imaging apparatus for cone beam computed tomography

ABSTRACT

Exemplary X-ray imaging systems (e.g., volume radiographic imaging systems, CBCT systems) and/or methods for using the same can provide a detector and a counterweight separately (e.g., scanner or gantry) even though the counterweight and the detector can be positioned in or traverse the same relative space.

FIELD OF THE INVENTION

The invention relates generally to diagnostic imaging and in particularto cone beam imaging systems used for obtaining volume images ofextremities.

BACKGROUND OF THE INVENTION

3-D volume imaging has proved to be a valuable diagnostic tool thatoffers significant advantages over earlier 2-D radiographic imagingtechniques for evaluating the condition of internal structures andorgans. 3-D imaging of a patient or other subject has been made possibleby a number of advancements, including the development of high-speedimaging detectors, such as digital radiography (DR) detectors thatenable multiple images to be taken in rapid succession.

Cone beam computed tomography (CBCT) or cone beam CT technology offersconsiderable promise as one type of diagnostic tool for providing 3-Dvolume images. Cone beam CT systems capture volumetric data sets byusing a high frame rate digital radiography (DR) detector and an x-raysource, typically affixed to a gantry that rotates about the object tobe imaged, directing, from various points along its orbit around thesubject, a divergent cone beam of x-rays toward the subject. The CBCTsystem captures projections throughout the rotation, for example, one2-D projection image at every degree of rotation. The projections arethen reconstructed into a 3D volume image using various techniques.Among well known methods for reconstructing the 3-D volume image fromthe 2-D image data are filtered back projection approaches.

Although 3-D images of diagnostic quality can be generated using CBCTsystems and technology, a number of technical challenges remain. In somecases, for example, there can be a limited range of angular rotation ofthe x-ray source and detector with respect to the subject. CBCT imagingof legs, arms, and other extremities can be hampered by physicalobstruction from a paired extremity. This is an obstacle that isencountered in obtaining CBCT image projections for the human leg orknee, for example. Not all imaging positions around the knee areaccessible; the patient's own anatomy often prevents the radiationsource and image detector from being positioned over a portion of thescan circumference.

To illustrate the problem faced in CBCT imaging of the knee, the topview of FIG. 1 shows the circular scan paths for a radiation source 22and detector 24 when imaging the right knee R of a patient as a subject20. Various positions of radiation source 22 and detector 24 are shownin dashed line form. Source 22, placed at some distance from the knee,can be positioned at different points over an arc of about 200 degrees;with any larger arc the paired extremity, left knee L, blocks the way.Detector 24, smaller than source 22 and typically placed very nearsubject 20, can be positioned between the patient's right and left kneesand is thus capable of positioning over the full circular orbit.

A full 360 degree orbit of the source and detector is not needed forconventional CBCT imaging; instead, sufficient information for imagereconstruction can be obtained with an orbital scan range that justexceeds 180 degrees by the angle of the cone beam itself, for example.However, in some cases it can be difficult to obtain much more thanabout 180 degree revolution for imaging the knee or other joints andother applications. Moreover, there can be diagnostic situations inwhich obtaining projection images over a certain range of angles hasadvantages, but patient anatomy blocks the source, detector, or bothfrom imaging over that range.

Still other difficulties with conventional solutions for extremityimaging relate to poor image quality. For image quality, the CBCTsequence requires that the detector be positioned close to the subjectand that the source of the cone beam radiation be at a sufficientdistance from the subject. This provides the best image and reducesimage truncation and consequent lost data. CBCT imaging represents anumber of challenges that also affect other types of volume imaging thatemploy a radiation source and detector orbiting an extremity over arange of angles. There are various tomographic imaging modes that can beused to obtain depth information for a scanned extremity.

In summary, for extremity imaging, particularly for imaging the lowerpaired extremities, a number of improvements are needed, including thefollowing:

-   (i) improved placement of the radiation source and detector relative    to the imaged subject to provide acceptable radiation levels and    image quality (e.g., reduced relative movement between a source and    a detector) throughout the scanning sequence, with the capability    for at least coarse automated setup for examining an extremity under    favorable conditions; or-   ii) improved patient accessibility, so that the patient does not    need to contort, twist, or unduly stress limbs or joints that may    have been injured in order to provide images of those body parts.

In summary, the capability for straightforward configuration andpositioning of the imaging apparatus allows the advantages of CBCTimaging to be adaptable for use with a range of extremities, to obtainvolume images under a suitable imaging modality, with the imageextremity presented at a suitable orientation under both load-bearingand non-load-bearing conditions, and with the patient appropriatelystanding or seated.

SUMMARY OF THE INVENTION

An aspect of this application is to advance the art of medical digitalradiography.

Another aspect of this application is to address, in whole or in part,at least the foregoing and other deficiencies in the related art.

It is another aspect of this application to provide, in whole or inpart, at least the advantages described herein.

It is another aspect of this application to advance the art ofdiagnostic imaging of extremity body parts, particularly jointed orload-bearing, paired extremities such as knees, legs, ankles, fingers,hands, wrists, elbows, arms, and shoulders.

It is another aspect of this application to provide apparatus and/ormethod embodiments that adapt to imaging conditions suitable for a rangeof extremities and/or allows the patient to be in a number of positionsfor suitable imaging of the extremity.

It is another aspect of this application to provide radiographic imagingapparatus and/or method embodiments that can separately provide adetector and a counterweight to a scan gantry mechanism.

It is another aspect of this application to provide radiographic imagingapparatus and/or method embodiments that can provide a detector andcounterweight configured to move independently from one another.

It is another aspect of this application to provide radiographic imagingapparatus and/or method embodiments that can provide two separatesupports individually for a detector and a counterweight that can allowdifferent materials or characteristics for the separate supports or thatcan reduce the total weight of materials from that used to position andsupport the detector and counterweight as a single unit.

It is another aspect of this application to provide radiographic imagingapparatus and/or method embodiments that can provide the ability toposition the detector relative to the source during scanning withreduced movement or vibration.

It is another aspect of this application to provide radiographic imagingapparatus and/or method embodiments that can provide a prescribed sizeclearance gap between a detector and a counterweight.

It is another aspect of this application to provide radiographic imagingapparatus and/or method embodiments that can provide separate supportsindividually for a detector and a counterweight to increase a scanvolume of a volumetric radiographic imaging system

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed invention may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings. The elements of the drawings are not necessarilyto scale relative to each other.

FIG. 1 is a schematic view showing the geometry and limitations of CBCTscanning for portions of the lower leg.

FIG. 2 shows a top and perspective view of the scanning pattern for animaging apparatus according to an embodiment of the application.

FIG. 3A is a perspective view showing patient access to an imagingapparatus according to an embodiment of the application.

FIG. 3B is a top view showing a sequence of steps for enclosing theextremity to be imaged within the path of the detector transport.

FIG. 3C is a perspective view showing patient access to another imagingapparatus according to an embodiment of the application.

FIG. 3D is a perspective view showing a revolvable gantry for anotherimaging apparatus according to an embodiment of the application.

FIG. 4 show portions of the operational sequence for obtaining CBCTprojections of a portion of a patient's leg at a number of angularpositions when using the imaging apparatus according to an embodiment ofthe application.

FIG. 5 is a perspective view that shows a CBCT imaging apparatus forextremity imaging according to an embodiment of the application.

FIG. 6A shows internal components used for imaging ring translation andpositioning.

FIG. 6B shows reference axes for rotation and translation.

FIG. 6C is a schematic diagram that shows components of the positioningsystem for the imaging scanner.

FIG. 6D is a perspective view showing some of the components of avertical translation apparatus.

FIG. 6E shows the CBCT imaging apparatus with covers installed.

FIG. 7A shows translation of the imaging ring with respect to a verticalor z-axis.

FIG. 7B shows rotation of the imaging ring about an αaxis that isorthogonal to the z-axis.

FIG. 7C shows rotation of the imaging ring about a γaxis that isorthogonal to the αaxis.

FIG. 7D shows the position of operator controls for fine-tune positionof the imaging scanner.

FIG. 7E shows an enlarged view of the positioning controls.

FIG. 8 is a perspective view that shows the extremity imaging apparatusconfigured for knee imaging with a standing patient.

FIG. 9 is a perspective view that shows the extremity imaging apparatusconfigured for foot or ankle imaging with a standing patient.

FIG. 10 is a perspective view that shows the extremity imaging apparatusconfigured for knee imaging with a seated patient.

FIG. 11 is a perspective view that shows the extremity imaging apparatusconfigured for elbow imaging with a seated patient.

FIG. 12A is a top view of the scanner components of an extremity imagingapparatus according to an embodiment of the application.

FIG. 12B is a perspective view of a frame that supports scannercomponents of an extremity imaging apparatus according to an embodimentof the application.

FIG. 12C is a perspective view of a frame that supports scannercomponents of an extremity imaging apparatus with added counterweightaccording to an embodiment of the application.

FIG. 13A is a top view of the imaging scanner showing the door openposition.

FIG. 13B is a perspective view of the imaging scanner showing a doorclosing position.

FIG. 13C is a top view of the imaging scanner showing the door closedposition.

FIG. 13D is a perspective view showing the door in closed position.

FIG. 14A is a top view of the imaging scanner with a number of itsinternal imaging components shown, at one extreme end of the imagingscan.

FIG. 14B is a top view of the imaging scanner with a number of itsinternal imaging components shown, at the opposite extreme end of theimaging scan from that shown in FIG. 14A.

FIG. 14C is a top view of the imaging scanner with its housing shown.

FIG. 14D is a top view of the imaging scanner with internal imagingcomponents and central arc angles shown.

FIG. 15 is a top view that shows movement of scanning components that isallowable when the door of the scanner is closed.

FIG. 16 is a perspective view of the scanner with the housing coversremoved, showing the door in closed position.

FIGS. 17A and 17B are diagrams that show additional features ofexemplary gantry and/or transport mechanism for use in CBCT X-rayimaging systems.

FIGS. 18A-18D are diagrams that show an exemplary embodiment of acounterweight support mechanism for use with a gantry for a transportmechanism for use in CBCT X-ray imaging systems according to theapplication.

FIGS. 19A-19B are diagrams that show an exemplary embodiment of acounterweight support mechanism for use with a gantry for a transportmechanism for use in CBCT radiographic imaging systems or the likeaccording to the application.

FIGS. 20A-20B are diagrams that show an exemplary embodiment of acounterweight support mechanism for use with a gantry for a transportmechanism for use in CBCT radiographic imaging systems or the likeaccording to the application.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following is a description of exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

For illustrative purposes, principles of the invention are describedherein by referring mainly to exemplary embodiments thereof. However,one of ordinary skill in the art would readily recognize that the sameprinciples are equally applicable to, and can be implemented in, alltypes of radiographic imaging arrays, various types of radiographicimaging apparatus and/or methods for using the same and that any suchvariations do not depart from the true spirit and scope of theapplication. Moreover, in the following description, references are madeto the accompanying figures, which illustrate specific exemplaryembodiments. Electrical, mechanical, logical and structural changes canbe made to the embodiments without departing from the spirit and scopeof the invention.

In the context of the application, the term “extremity” has its meaningas conventionally understood in diagnostic imaging parlance, referringto knees, legs, ankles, fingers, hands, wrists, elbows, arms, andshoulders and any other anatomical extremity. The term “subject” is usedto describe the extremity of the patient that is imaged, such as the“subject leg”, for example. The term “paired extremity” is used ingeneral to refer to any anatomical extremity wherein normally two ormore are present on the same patient. In the context of the application,the paired extremity is not imaged unless necessary; only the subjectextremity is imaged. In one embodiment, a paired extremity is not imagedto reduce patient dose.

A number of the examples given herein for extemporary embodiments of theapplication focus on imaging of the load-bearing lower extremities ofthe human anatomy, such as the leg, the knee, the ankle, and the foot,for example. However, these examples are considered to be illustrativeand non-limiting.

In the context of the application, the term “arc” or, alternately, orarcuate has a meaning of a portion of a curve, spline or non-linearpath, for example as being a portion of a curve of less than or greaterthan 360 degrees.

The term “actuable” has its conventional meaning, relating to a deviceor component that is capable of effecting an action in response to astimulus, such as in response to an electrical signal, for example.

As used herein, the term “energizable” relates to a device or set ofcomponents that perform an indicated function upon receiving power and,optionally, upon receiving an enabling signal.

In the context of the application, two elements are considered to besubstantially orthogonal if their angular orientations differ from eachother by 90 degrees, +/− no more than about 10 degrees. It isinstructive to observe that the mathematical definition of a cylinderincludes not only the familiar “can-shaped” right circular cylinder, butalso any number of other shapes. The outer surface of a cylinder isgenerated by moving a first straight line element along a closed curveor other path along a base plane, while maintaining the first straightline element parallel to a second, fixed straight line that extends outfrom the base plane, wherein the moving first straight line intersects afixed closed curve or base in the base plane. A cube, for example, isconsidered to have a cylindrical shape according to this definition. Acan-shaped cylinder of revolution, for example, is generated when themoving first straight line intersects a circle in the base plane at aright angle. An object is considered to be substantially cylindricalwhen its overall surface shape is approximated by a cylinder shapeaccording to this definition, with allowance for standard edge rounding,protruding or recessed mechanical and electrical fasteners, and externalmounting features.

Certain exemplary embodiments according to the application address thedifficulties of extremity imaging by providing an imaging apparatus thatdefines coordinated non-linear source and detector paths (e.g., orbital,curved, or concentric about a center point), wherein components thatprovide the source and detector paths are configured to allow patientaccess prior to and following imaging and configured to allow thepatient to sit or stand with normal posture during the CBCT imagecapture series. Certain exemplary embodiments provide this capability byusing a detector transport device that has a circumferential accessopening allowing positioning of the extremity, wherein the detectortransport device is revolved about the positioned extremity once it isin place, enclosing (e.g., partially, substantially, fully) theextremity as it is revolved through at least a portion of the scan.

It is instructive to consider dimensional attributes of the human framethat can be considerations for design of CBCT equipment for scanningextremities. For example, an adult human patient of average height in acomfortable standing position has left and right knees generallyanywhere from about 10 to about 35 cm apart. For an adult of averageheight, exceeding about 35-40 cm (14-15.7 inches) between the kneesbecomes increasing less comfortable and out of the range of normalstanding posture. It is instructive to note that this constraint makesit impractical to use conventional gantry solutions for obtaining theneeded 2-D image sequence. For certain exemplary embodiments, either thesource or the detector must be able to pass between the legs of astanding patient for knee CBCT imaging, a capability not available withgantry or other conventional solutions.

The perspective and corresponding top views of FIG. 2 show how thescanning pattern is provided for components of CBCT imaging apparatus 10according to an embodiment of the application. A detector path 28 of asuitable radius R1 from a central axis β is provided for a detectordevice by a detector transport 34. A source path 26 of a second, largerradius R2 is provided for a radiation source by a source transport 32.In one embodiment, a non-linear source path 26 is greater in length thana non-linear detector path 24. According to an embodiment of theapplication, described in more detail subsequently, the same transportsystem provides both detector transport 34 and source transport 32. Theextremity, subject 20, is preferably substantially centered alongcentral axis β so that central axis β can be considered as a linethrough points in subject 20. In one embodiment, an imaging bore or theCBCT apparatus can include or encompass the central axis β. The limitinggeometry for image capture is due to the path of source transport 32,blocked by gap 38 (e.g., for patient anatomy, such as by a paired limb),and thus limited typically to less than about 220 degrees, as notedpreviously. The circumferential gap or opening 38 can occupy the spacebetween the endpoints of the arc of source path 26. Gap or opening 38gives space for the patient a place to stand, for example, while one legis being imaged.

Detector path 28 can extend through circumferential gap 38 to allowscanning, since the detector is not necessarily blocked by patientanatomy but can have a travel path at least partially around an imagedextremity that can extend between the standing patient's legs.Embodiments of the present invention allow temporary restriction of thedetector path 28 to allow access for the patient as part of initialpatient positioning. The perspective view in FIG. 2, for example, showsdetector transport 34 rotated to open up circumferential gap 38 so thatit extends from the axis β (e.g., beyond a source path or housing). Withdetector transport 34 translated to the open position shown in FIG. 3A,the patient can freely move in and out of position for imaging. When thepatient is properly in position, detector transport 34 is revolved aboutaxis βby more than 180 degrees; according to an embodiment of theapplication, detector transport 34 is revolved about axis β bysubstantially 200 degrees. This patient access and subsequent adjustmentof detector transport 34 is shown in successive stages in FIG. 3B. Thisorbital movement confines the extremity to be imaged more effectivelyand places detector 24, not visible in FIGS. 2-3C due to the detectortransport 34 housing, in position near subject 20 for obtaining thefirst projection image in sequence. In one embodiment, a detectortransport 34 can include shielding or a door over part of the detectorpath, and/or the gap 38. As shown in FIG. 3D, a revolvable gantry 68allows detector 24 and source 22 to revolve around imaging volume ofanother imaging apparatus 10′ according to an embodiment of theapplication.

Circumferential gap or opening 38 not only allows access for positioningof the subject leg or other extremity, but also allows sufficient spacefor the patient to stand in normal posture during imaging, placing thesubject leg for imaging in the central position along axis α (FIG. 2)and the non-imaged paired leg within the space defined bycircumferential gap 38. Circumferential gap or opening 38 extendsapproximately 180 degrees minus the fan angle (e.g., between ends of thesource path), which is determined by source-detector geometry anddistance. Circumferential gap or opening 38 permits access of theextremity so that it can be centered in position along central axis β.Once the patient's leg or other extremity is in place, detectortransport 34, or a hooded cover or hollow door or other member thatdefines this transport path, can be revolved into position, closing thedetector portion of circumferential gap or opening 38.

By way of example, the top views of FIG. 4 show portions of theoperational sequence for obtaining CBCT projections of a portion of apatient's leg at a number of angular positions when using a CBCT imagingapparatus. The relative positions of radiation source 22 and detector24, which may be concealed under a hood or chassis, as noted earlier,are shown in FIG. 4. The source 22 and detector 24 can be aligned so theradiation source 22 can direct radiation toward the detector 24 (e.g.,diametrically opposite) at each position during the CBCT scan andprojection imaging. The sequence begins at a begin scan position 50,with radiation source 22 and detector 24 at initial positions to obtainan image at a first angle. Then, both radiation source 22 and detector24 revolve about axis β (e.g., imaging volume) as represented in interimscan positions 52, 54, 56, and 58. Imaging terminates at an end scanposition 60. As this sequence shows, source 22 and detector 24 are inopposing positions relative to subject 20 at each imaging angle.Throughout the scanning cycle, detector 24 is within a short distance D1of subject 20. Source 22 is positioned beyond a longer distance D2 ofsubject 20.

The positioning of source 22 and detector 24 components on each path canbe carried out by separate actuators, one for each transport path, or bya single rotatable member, as described in more detail subsequently. Itshould be noted that scanning motion in the opposite direction, that is,clockwise with respect to the example shown in FIG. 4, is also possible,with the corresponding changes in initial and terminal scan positions.

Given this basic operation sequence in which the source 22 and detector24 orbit the extremity, the usefulness of an imaging system that isadaptable for imaging patient extremities with the patient sitting orstanding and in load-bearing or non load-bearing postures can beappreciated. The perspective view of FIG. 5 shows a CBCT imagingapparatus 100 for extremity imaging according to an embodiment of theapplication. Imaging apparatus 100 has a gimballed imaging ring orscanner 110 that houses and conceals source 22 and detector 24 within ahousing 78. FIG. 5 shows their supporting transport mechanisms. Scanner110 is adjustable in height and rotatable in gimbaled fashion aboutnon-parallel axes, such as about substantially orthogonal axes asdescribed in subsequent figures, to adapt to various patient posturesand extremity imaging conditions. A support column 120 supports scanner110 on a yoke, or bifurcated or forked support arm 130, a rigidsupporting element that has adjustable height and further providesrotation of scanner 110 as described subsequently. Support column 120can be fixed in position, such as mounted to a floor, wall, or ceiling.According to portable CBCT embodiments such as shown in FIG. 6A andelsewhere, support column 120 mounts to a support base 121 that alsoincludes optional wheels or casters 122 for transporting and maneuveringimaging apparatus 100 into position. A control panel 124 can provide anoperator interface, such as a display monitor, for entering instructionsfor apparatus 100 adjustment and operation. In one embodiment, thecontrol panel 124 can include a processor or computer (e.g., hardware,firmware and/or software) to control operations of the CBCT system 100.Support column 120 can be of fixed height or may have telescopingoperation, such as for improved visibility when apparatus 100 is moved.

Vertical and Rotational Movement

FIG. 6A shows portions of exemplary internal imaging and positioningmechanisms (with covers removed) for scanner 110 that allow imagingapparatus 100 the capability for imaging extremities with a variety ofconfigurations. FIG. 6B shows rotation axes definitions for scanner 110positioning. The α-axis and the γ-axis are non-parallel, to allowgimbaled action. According to an embodiment of the application as shownin FIG. 6A, the α-axis and the γ-axis are mutually orthogonal. Theα-axis is substantially orthogonal to the z-axis. The intersection ofthe αaxis and the γ-axis can be offset from support column 120 by somenon-zero distance.

First considering the z-axis, FIG. 6A shows an exemplary embodiment toachieve vertical motion. Within support column 120, a vertical carriagetranslation element 128 is actuated in order to travel upwards ordownwards along column 120 within a track 112 in a vertical direction.Carriage translation element 128 has a support shaft 132 that is coupledto an actuator 136 for providing α-axis rotation to forked or C-shapedsupport arm 130. Forked support arm 130, shown only partially in FIG. 6Ato allow a better view of underlying components, is coupled to supportshaft 132. X-ray source 22 and receiver 24 are mounted on a rotatablegantry 36 for rotation about a scan or central axis, designated as the βaxis. Axis β is orthogonal to the α-axis and the γ-axis.

It can be appreciated that z-axis translation can be effected in anumber of ways. Challenges that must be addressed by the type of systemthat is used include handling the weight of forked support arm 130 andthe imaging scanner 110 that arm 130 supports. This can easily weigh afew hundred pounds. In addition, precautions must be provided forhandling conditions such as power loss, contact with the patient, ormechanical problems that hamper positioning movement or operation.According to an embodiment of the application, as shown schematically inFIG. 6C and in the perspective view of FIG. 6D, a vertical actuator 129rotates a threaded shaft 123. Vertical carriage translation element 128employs a ball screw mount apparatus 125 to translate rotational motionto the needed linear (e.g., z-direction) motion, thus urging verticalcarriage translation element 128 upward or allowing vertical carriagetranslation element 128 to move downward. Ball screw translation devicesare advantaged for handling high weight loads and are typically moreefficient than other types of translators using threaded devices. Theuse of a ball screw arrangement also allows a small motor to drive theshaft that lifts scanner 110 into position and can help to eliminate theneed for a complex and bulky counterweight system for allowing controlof vertical movement. An encoder 145, such as a linear encoder element,can provide feedback signals that are used to indicate the verticalposition of vertical carriage translation element 128.

Vertical carriage translation element 128 travels inside track 112formed in support column 120 (FIG. 6A); wheels 138 help to guidetranslation element 128 within the slots. Paired wheels 138 can beorthogonal to each other to provide centering within column 120.

A braking system can also be provided for support column 120.Spring-loaded brakes 142 (FIG. 6D) are positioned to actuate and gripshaft 123 or other mechanical support when mechanical difficulties,power failure, or other conditions are detected. A sensor 144, such as aload cell, is configured to sense rapid movement or interferenceconditions that are undesirable and to cause brakes 142 actuation.

Other features of support column 120 for vertical translation includebuilt-in redundancy, with springs to absorb weight and impact, the loadcell to sense a mechanical problem including obstruction by the patient,and manually operable brake mechanisms.

It should be noted that other types of translation apparatus could beused for providing vertical movement of vertical carriage translationelement 128. In one embodiment, the β-axis can be implemented +/− up to10 degrees. In one embodiment, the horizontal 60 -axis can beimplemented +/− up to 10 degrees. In one embodiment, the γ-axis for aCBCT apparatus can be +/− up to 45 degrees.

Gimbaled Arrangement for Scanner

Forked support arm 130 can support scanner 110 in a gimbaledarrangement. Source 22 and detector 24 are shown on gantry 36 forreference in FIG. 6A and covered in the alternate view of FIG. 6E.Vertical carriage translation element 128 is configured to ride within atrack 112 (FIG. 6A) within support column 120. For certain exemplaryembodiments, some level of manual operability can be provided, such asfor power loss situations.

According to an alternate embodiment of the application, verticalcarriage translation element 128 can be a motor that moves verticallyalong supporting threaded shaft 132; alternately, vertical carriagetranslation element 128 can be driven using a chain, pulley, or otherintermediate mechanism that has considerable counterweights for manuallyraising and lowering vertical carriage translation element 128 and itsconnected forked support arm 130 and components within support column120.

Next, considering the α-axis movement of forked support arm 130, in oneembodiment a rotational actuator 136 can be energizable to allowrotation of shaft 132 (FIG. 6A). This rotational actuation can beconcurrent with z-axis translation as well as with rotation with respectto the γ-axis.

Forked support arm 130 allows movement relative to the γ-axis accordingto the position and angle of forked support arm 130. In the example ofFIG. 6A, the γ-axis is oriented vertically, substantially in parallelwith the z-axis. FIG. 6E shows the γ-axis oriented horizontally. Apivoting mount 140 with a rotational actuator 146, provided by forkedsupport arm 130, allows rotation along the γ-axis. The gimbaledcombination of α-axis and γ-axis rotation can allow the imagingapparatus to be set up for imaging in a number of possible positions,with the patient standing, seated, or prone.

An exemplary positioning capability of the imaging apparatus 100 isshown in FIGS. 7A-7C. FIG. 7A shows movement of forked support arm 130on support column 120 to provide z-axis (vertical) translation ofscanner 110. FIG. 7B shows rotation of forked support arm 130 about thehorizontal α-axis. FIG. 7C shows rotation about the γ-axis as defined bythe C-arm arrangement of forked support arm 130.

Sequence and Controls for Positioning Support Arm 130

According to an exemplary embodiment, an initial set of operatorcommands automatically configure CBCT imaging apparatus 100 to one of awell-defined set of default positions for imaging, such as thosedescribed subsequently. The patient waits until this initial setup iscompleted. Then, the patient is positioned at CBCT imaging apparatus 100and any needed adjustments in height (z-axis) or rotation about the α orγ axes can be made by the technician. This type of fine-tuningadjustment is at slow speeds for increased patient comfort and becauseonly incremental changes to position are needed in most cases.

FIG. 7D and the enlarged view of FIG. 7E show user control stations 156,158 that are provided on arm 130 (with scanner 110 removed for improvedvisibility) for operator adjustment of z-axis translation and α-andγ-axis rotation as described in FIGS. 7A-7C. Both control stations 156and 158 are essentially the same, duplicated to allow easier access forthe operator for different extremity imaging arrangements. By way ofexample, FIG. 7E shows an enlarged view of control station 158. Anenablement switch 159 is pressed to activate a control 160 and anassociated indicator illuminates when control 160 is active or enabled.As a patient safety feature to protect from inadvertent patient contactwith the controls in some imaging configurations, one or both controlstations 156, 158 are disabled. One or both control stations 156, 158can also be disabled following a time-out period after switch 159 hasbeen pressed. An emergency stop control 162 can stop all motion of theimaging apparatus including downward motion of support arm 130.

Still referring to FIG. 7E, control 160 can activate any of theappropriate actuators for z-axis translation, α-axis rotation and/orγ-axis rotation. Exemplary responses of the system can be based onoperator action, as follows:

-   (i) z-axis vertical movement is effected by pressing control 160 in    a vertical upward or downward direction. The control logic adjusts    for the angular position of the support arm 130, so that pressing    the control upward provides z-axis movement regardless of support    arm 130 orientation.-   (ii) α-axis rotation is effected by rotating control 160. Circular    motion of control 60 in an either clockwise (CW) or counterclockwise    (CCW) direction causes corresponding rotation about the α axis.-   (iii) γ-axis rotation is effected by horizontal left-to-right or    right-to-left movement of control 60. As with z-axis movement,    control logic adjusts for the angular position of the support arm    130, so that left-right or right-left movement is relative to the    operator regardless of support arm 130 orientation.

It should be noted that CBCT imaging apparatus 100 as shown in FIG. 6Eprovides at least three degrees of freedom (DOF) for scanner 110positioning. In addition to the z-axis translation and rotation about α-and γ-axes previously described, casters 122 allow rotation of scanner110 position with respect to the z-axis as well as translation along thefloor.

Configurations for Imaging Various Extremities

Given the basic structure described with reference to FIGS. 6A-7D, thepositioning versatility of scanner 110 for various purposes can beappreciated. Subsequent FIGS. 8-11 show, by way of example, how thisarrangement serves different configurations for extremity imaging.

FIG. 8 shows an exemplary scanner 110 positioning for a knee exam, wheresubject 20 is a standing patient. An optional patient support bar 150can be attached to support column 120. In one embodiment, support bar150 is mounted to vertical carriage translation element 128.Accordingly, as the vertical carriage translation element 128 moves, acorresponding position of the support bar 150 can be moved. According toan alternate embodiment of the application, the support bar 150 can bemounted to the scanner 110, such as to the cover of scanner 110 or tothe forked support arm 130. In contrast, embodiments of support bar 150can be motionless during imaging or during a scan by the scanner 110.For this embodiment, vertical adjustment along the z-axis sets the kneeof the patient at the center of the scanner 110. Forked support arm 130is arranged so that the plane that contains both the α-axis and theγ-axis is substantially horizontal. Patient access is through anopening, circumferential gap or opening 38 in scanner 110. A door 160 ispivoted into place across gap 38 to enclose an inner portion ofcircumferential gap or opening 38. Door 160 fits between the legs of thepatient once the knee of the patient is positioned.

Certain exemplary embodiments of optional patient support bar 150 can bemounted to movable portions of the CBCT apparatus 100, preferably tohave a prescribed spatial relationship to an imaging volume. For suchembodiments, a presence detector 151 can be configured to detect whenthe support bar 150 is mounted to the CBCT system 100. When detected, acontroller or the like, for example, in the control panel 124, cancalculate scanner 110, and/or forked support arm 130 movements toprevent collisions therebetween with the affixed support bar 150. Thuswhen attached, support bar 150 can limit motion of the scanner 110.Exemplary presence detectors 151 can include but are not limited tomagnetic detectors, optical detectors, electro-mechanical detectors orthe like. As shown in FIG. 9, a pair of optional or removable supportarms 150 can be affixed to the vertical carriage translation element 128and have their attachment reported by a pair of presence detectors 151.

For FIG. 8 and selected subsequent exemplary embodiments, door 160, oncepivoted into its closed position, can effectively extend the imagingpath by protecting and/or providing the curved detector transport 34path as shown in FIG. 4. With this arrangement, when door 160 is closedto protect the transport path, the knee can be examined underweight-bearing or non-weight-bearing conditions. By enclosing theportion of detector transport 34 path that crosses opening 38, door 160enables the extremity to be positioned suitably for 3D imaging and to bemaintained in position between the source and detector as these imagingcomponents orbit the extremity in the CBCT image capture sequence.

FIG. 9 shows scanner 110 positioning for a foot or ankle exam whereinsubject 20 is a standing patient. With this configuration, scanner 110is lowered to more effectively scan the area of interest. The plane thatcontains both the α-axis and the γ-axis is approximately 10 degreesoffset from horizontal, rotated about the γ axis. A step 116 is providedacross circumferential gap or opening 38 for patient access.

FIG. 10 shows scanner 110 positioning for a knee exam with the patientseated. For this configuration, forked support arm 130 is elevated withrespect to the z-axis. Rotation about the α-axis orients the γ-axis sothat it is vertical or nearly vertical. Circumferential gap or opening38 is positioned to allow easy patient access for imaging the rightknee. It should be noted that 180 degree rotation about the γ-axis wouldposition circumferential gap or opening 38 on the other side of scanner110 and allow imaging of the other (left) knee.

Alternative scanner 110 positioning can include foot or ankle exam withthe patient seated, toe exam with the patient seated, a hand exam, withthe patient seated.

FIG. 11 shows scanner 110 positioning for an elbow exam, with thepatient seated. For this configuration, forked support arm 130 is againelevated with respect to the z-axis. Rotation about the γ-axis positionscircumferential gap 38 suitably for patient access. Further rotationabout the α-axis may be provided for patient comfort.

In one embodiment of CBCT imaging apparatus 100, the operator can firstenter an instruction at the control console or control panel 124 thatspecifies the exam type (e.g., for the configurations shown in FIGS.8-11). The system then automatically adapts the chosen configuration,prior to positioning the patient. Once the patient is in place, manuallycontrolled adjustments to z-axis and α- and γ-axes rotations can bemade, as described previously.

Scanner Configuration and Operation

As previously described with reference to FIGS. 1-4, scanner 110 isconfigured to provide suitable travel paths for radiation source 22 anddetector 24 about the extremity that is to be imaged, such as thoseshown in FIGS. 8-11. Scanner 110 operations in such various exemplaryconfigurations can present a number of requirements that can be at leastsomewhat in conflict, including the following:

-   (i) Imaging over a large range of angles, preferably over an arc    exceeding 180 degrees plus the fan angle of the radiation source.-   (ii) Ease of patient access and extremity positioning for a wide    range of limbs.-   (iii) Capability to allow both weight-bearing and non-weight-bearing    postures that allow imaging with minimized strain on the patient.-   (iii) Enclosure to prevent inadvertent patient contact with moving    parts.-   (iv) Fixed registration of source to detector throughout the scan    cycle.

The top view of FIG. 12A shows a configuration of components of scanner110 that orbit subject 20 according to an exemplary embodiment of theapplication. One or more sources 22 and detector 24 are mounted in acantilevered C-shaped gantry 36 that is part of a transport assembly 170that can be controllably revolved (e.g., rotatable over an arc aboutcentral axis α). Source 22 and detector 24 are thus fixed relative toeach other throughout their movement cycle. An actuator 172 is mountedto a frame 174 of assembly 170 and provides a moving hinge for gantrypivoting. Actuator 172 is energizable to move gantry 36 and frame 174with clockwise (CW) or counterclockwise (CCW) rotation as needed for thescan sequence. Cover 184 can reduce or keeps out dust and debris and/orbetter protect the operator and patient from contact with moving parts.

The perspective view of FIG. 12B shows frame 174 and gantry 36 oftransport assembly 170 in added detail. Actuator 172 cooperates with abelt 178 to pivot frame 174 for moving source 22 and detector 24 aboutaxis α. The perspective view of FIG. 12C shows frame 174 with addedcounterweights 182 for improved balance of the cantilevered arrangement.

Because a portion of the scan arc that is detector path 28 (FIG. 2)passes through the circumferential gap or opening 38 that allows patientaccess, this portion of the scan path should be isolated from thepatient. FIGS. 13A, 13B, and 13C show, in successive positions forclosing over gap or opening 38, a slidable door 176 that is stored in aretracted position within a housing 180 for providing a covering overthe detector path 28 once the patient is in proper position. In oneembodiment, door 176 can be substantially a hollow structure that, whenclosed, allows passage of the detector 24 around the patient'sextremity. Referring to FIG. 12B, the portion of frame 174 of gantry 36that supports detector 24 can pass through the hollow inner chamberprovided by door 176 during the imaging scan. At the conclusion of theimaging sequence, frame 174 of gantry 36 rotates back into its homeposition and door 176 is retracted to its original position for patientaccess or egress within housing 180. In one embodiment, the door 176 ismanually opened and closed by the operator. In one embodiment,interlocks are provided so that movement of scanning transportcomponents (rotation of cantilevered frame 174) is only possible whilefull closure of the door 176 is sensed.

FIG. 13B also shows top and bottom surfaces 190 and 192, respectively,of housing 180. An outer circumferential surface 194 extends between andconnects top and bottom surfaces 190 and 192. An inner circumferentialsurface 196 is configured to connect the top and bottom surfaces 190 and192 to form a central opening 198 extending from the first surface tothe second surface, where the central opening 198 surrounds the αaxis.

As shown with respect to FIGS. 2 and 4, in one embodiment radiationsource 22 and detector 24 each can orbit the subject along an arc withradii R2 and R1, respectively. According to an alternate embodiment,within source transport 32, a source actuator could be used, cooperatingwith a separate, complementary detector actuator that is part ofdetector transport 34. Thus, two independent actuator devices, one ineach transport assembly, can be separately controlled and coordinated byan external logic controller to move source 22 and detector 24 alongtheir respective arcs, in unison, about subject 20.

In the context of the present disclosure, a surface is considered to be“substantially” flat if it has a radius of curvature that exceeds about10 feet.

The perspective view of FIG. 10 shows the extremity CBCT imagingapparatus 100 configured for knee imaging with a seated patient. FromFIG. 10, it can be seen that the patient needs room outside of the scanvolume for comfortable placement of the leg that is not being imaged.For this purpose, housing 78 is shaped to provide additional clearance.

As is readily visible from FIGS. 8-11 and 13A-13D, imaging scanner 110has a housing 78. According to one embodiment of the application,housing 78 is substantially cylindrical; however, a cylindrical surfaceshape for housing 78 is not required. By substantially cylindrical ismeant that, to at least a first approximation, the housing 78 surfaceshape closely approximates a cylinder, with some divergence from strictgeometric definition of a cylinder and with a peripherally gap and someadditional features for attachment and component interface that are notin themselves cylindrical.

FIGS. 14A-14D show a number of features that are of interest for anunderstanding of how scanner 110 is configured and operated (e.g.,scans). FIG. 14A shows how peripheral gap 38 is formed by housing 78,according to an embodiment of the application. Scan volume 228, outlinedwith a dashed line, is defined by the source and detector paths 26 and28, as described previously, and typically includes at least a portionof the αaxis. An inner central volume 230 can be defined by surface S2of housing 78 and can typically enclose scan volume 228. Inner centralvolume 230 can also be defined by door 176 when closed, as shown in FIG.14C. Peripheral gap 38 is contiguous with inner central volume 230 whendoor 176 is in open position (e.g., fully or partially opened).

FIG. 14A shows source transport 32 and detector transport 34 at oneextreme end of the scan path, which may be at either the beginning orthe end of the scan. FIG. 14B shows source transport 32 and detectortransport 34 at the other extreme end of the scan path. It should benoted that source 22 is offset along source transport 32. With thisasymmetry, the extent of travel of source 22 relative to surface S3 ofhousing 78 differs from its extent of travel relative to surface S4. Atthe extreme travel position shown in FIG. 14B, source 22 is more thantwice the distance from surface S4 as source 22 is from surface S3 atthe other extreme travel position shown in FIG. 14A. In one embodiment,the inventors use this difference to gain additional clearance forpatient positioning with the patient seated.

FIG. 14C shows the configuration of housing 78. In the context of thepresent disclosure, top surface 190 is considered to be aligned with thetop of, at least partially above, or above scan volume 228; bottomsurface 192 is aligned with the bottom of, at least partially below, orbelow scan volume 228. In one embodiment, the top surface 190 or thebottom surface 192 can intersect a portion of the scan volume 228. Asshown in FIG. 14C, scan volume 228 can be cylindrical or circularlycylindrical. However, exemplary embodiments of the application areintended to be used with other known 2D scan areas and/or 3D scanvolumes. The cover of housing 78 can be metal, fiberglass, plastic, orother suitable material. According to an embodiment, at least portionsof top and bottom surfaces 190 and 192 are substantially flat.

As shown in FIGS. 14A-14C, the scanner 110 has a number of surfaces thatdefine its shape and the shape of peripheral gap or opening 38:

-   (i) an outer connecting surface S1 extends between a portion of top    surface 190 and a portion of bottom surface 192 to at least    partially encompass the source and detector; at least a portion of    the outer connecting surface extends outside the path the source    travels while scanning; embodiments of the outer connecting surface    S1 shown in FIGS. 14A-14C provide an arcuate surface that is    generally circular at a radius R5 about center 13 and that extends,    between edges E1 and E2 of the housing;-   (ii) an inner connecting surface S2 extends between a portion of the    first surface and a portion of the second surface to define an inner    central volume 230 that includes a portion of scan volume 228; in    the embodiment shown in FIG. 14D, inner connecting surface S2 is    approximately at a radius R4 from the β axis. At least portions of    inner connecting surface S2 can be cylindrical.-   (iii) other connecting surfaces can optionally include a surface S3    that corresponds to a first endpoint of the travel path for source    transport 32 (FIGS. 14A-14B) and is adjacent to curved surface S1    along an edge El, wherein surface S3 extends inward toward curved    inner surface S2; and a surface S4 that corresponds to a second    endpoint at the extreme opposite end of the travel path from the    first endpoint for source transport 32 and is adjacent to curved    surface S1 along an edge E2 wherein surface S4 extends inward toward    curved inner surface S2. According to an embodiment, surfaces S3 and    S4 are substantially flat and the angle between surfaces S3 and S4    is greater than about 90 degrees. In general, other additional    surface segments (e.g., short linear or curved surface segments) may    extend between or comprise any of surfaces S1-S4.

Inner and outer connecting surfaces S1, S2, and, optionally, othersurfaces, define peripheral gap or opening 38 that is contiguous withthe inner central volume 230 and extends outward to intersect the outerconnecting surface S1 to form gap 38 as an angular recess extending frombeyond or toward where the outer connecting surface S1 would, ifextended, cross the opening 38. As shown in FIG. 14D, a central angle ofa first arc A1 that is defined with a center located within the scanvolume and between edges of the peripheral gap 38 determined at a firstradial distance R4 outside the scan volume is less than a central angleof a second arc A2 that is defined with the first arc center and betweenthe edges of the peripheral gap 38 at a second radial distance R3outside the scan volume, where the second radial distance R3 is greaterthan the first radial distance R4. In one embodiment, as shown in FIG.14D, a first distance that is defined between edges of the peripheralgap 38 determined at a first radial distance R4 outside the scan volumeis less than a second distance between the edges of the peripheral gap38 at a second radial distance R3 outside the scan volume, where thesecond radial distance R3 is greater than the first radial distance R4.According to one embodiment, arcs A1 and A2 are centered about the 13axis, as shown in FIG. 14D and edges of gap 38 are defined, in part, bysurfaces S3 and S4 of housing 78.

The needed room for patient anatomy, such as that described withreference to FIG. 10, can be provided when the central angle for arc A2is large enough to accommodate the extremity that is to be imaged.According to one embodiment, the central angle for arc A2 between edgesof gap 38 exceeds the central angle for arc A1 by at least about 5degrees; more advantageously, the central angle for arc A2 exceeds thecentral angle for arc A1 by at least about 10 or 15 degrees.

The perspective views of FIGS. 8-11 show various configurations ofextremity CBCT imaging apparatus 100 for imaging limbs of a patient. Foreach of these configurations, the limb or other extremity of the patientmust be positioned at the center of scanner 110 and space must beprovided for the paired extremity. As described herein, peripheral gapor opening 38 is provided to allow access space for the patient and roomfor other parts of the patient anatomy. Door 176 is withdrawn into thehousing 78 until the patient is positioned; then, door 176 is pivotedinto place in order to provide a suitable transport path for the imagingreceiver, detector 24, isolated from the patient being imaged.

FIG. 13A shows scanner 110 with door 176 in open position, notobstructing opening 38, that is, keeping opening 38 clear, allowingpatient access for extremity placement within opening 38. FIG. 13C is atop view that shows scanner 110 with door 176 in closed position, heldby a latch 92. Door 176 thus extends into the opening 38, enclosing aportion of opening 38 for imaging of the patient's extremity. A sensor82 provides an interlock signal that indicates at least whether door 176is in closed position or in some other position. Movement of internalscanner 110 components such as C-shaped gantry 36 is prevented unlessthe door 176 is latched shut. A release 90 unlatches door 176 from itslatched position. As shown in FIGS. 13C and 13D, handle 76 can bepositioned outside of opening 38, such as along surface 51 as shown, foropening or closing door 176. Placement of handle 76, or other type ofdoor closure device, outside of opening 38 is advantageous for patientcomfort when closing or opening door 176. As shown in the exemplaryembodiment of FIGS. 13C and 13D, handle 76 is operatively coupled withdoor 176 so that movement of handle 76 in a prescribed direction, suchas along the circumference of scanner 110 housing 78 (e.g., acorresponding direction, or in the clockwise direction shown), causesdoor 176 corresponding movement (e.g., in the same direction). In oneembodiment, clockwise movement of handle 76 causes clockwise movement ofdoor 176, extends door 176 into the opening, and closes door 176;counterclockwise movement of handle 76 causes counterclockwise movementof door 176 and opens door 176, so that it does not obstruct the openingor moves to a position that is clear of the opening.

According to one embodiment, the door 176 is manually pivoted, closed,and opened by the operator. This allows the operator to more carefullysupport the patient and the extremity that is to be imaged. According toan alternate embodiment, an actuator is provided to close or open thedoor automatically.

FIG. 15 shows the initial position of gantry 36 at an angle θ0 when door176 has just been closed. Source 22 and detector 24 are at a rest ordefault position at angle θ0. Detector path 28 extends into the hollowportion of door 176 as shown.

FIG. 15 shows, from a top view, the relative angular rotation of gantry36 and how the hollow passage 84 provided by door 176 allows a wideangular range of travel for the orbit of detector 24 around the subjectbeing imaged within the scan volume 228. This sequence shows how door176 covers or surrounds, but does not obstruct, detector path 28 andshows how detector path 28 passes through the hollow interior of door176 for imaging when the patient is appropriately positioned and door176 is pivoted into place and latched. According to an alternateembodiment, another feature of door 176 is a closure portion 188 thatcan cover a door aperture 88 in housing 78 before, during and followingdoor closing.

The perspective view of FIG. 16, with the cover of housing 78 removedfor visibility of internal parts, shows another feature of door 176. Aclosure portion 188 is provided as a part of door 176 to cover the gapthat would otherwise be exposed when the door was closed. This coveringkeeps out dirt and debris and helps to prevent patient contact with, andvisibility of, internal moving parts of scanner 110. According to analternate embodiment, an edge 94 of closure portion 188 is attached tohousing 78 and closure portion 188 folds or bends into place as door 176pivots toward its closed position.

As shown in FIG. 6A, the source 22 and the detector 24 on the gantry 36run on a portion of an arcuate non-linear guide rail (e.g., slot).However, the mass of a radiation source can be 5×, 10×, 20× or morerelative to the mass of a radiation detector. In exemplary CBCT X-rayimaging systems, the combination of the uneven source 22 and detector 24masses and/or the position of the masses relative to a scanning volumeor a center of rotation (e.g., β axis) can create a large imbalance. Forexample, the unbalanced CBCT gantry mechanism can suffer backlash whenthe source “tips over” a high position (or low position) of tilted scangeometry.

Accordingly, a counterweight can be added to a detector to move thecenter of gravity (COG) of a scanner (e.g., scanner 110 or gantry 36)closer to the scanning volume or center of rotation and/or to reduce themass imbalance of the source and detector. FIGS. 12C, 16, 17A and 17Bshow the counterweight 182 added to the detector 24. A counterweightbeing added to a detector can provide advantages for motion control suchas but not limited to (i) a force to drive the counter-balanced gantryin all orientations can be reduced, (ii) inertia can be increased andcan be more easily controlled and/or (iii) vibration (e.g., between thesource and detector) during motion or scanning of the scan volume can bereduced.

A counterweight can include disadvantages to CBCT X-ray imaging systemsand/or methods with the more balanced gantry. Preferably, the source 22and the detector 24 do not move relative to one another during scanningof the scan volume 228. Accordingly, a very strong structure is neededto withstand the bending forces created and/or applied to a gantry 36 bythe counterweight 182 (and/or source 22, detector 24). Further, thestructure must be sufficient to move the radiation source and detector(with counterweight) in unison.

FIGS. 17A and 17B are diagrams that show additional features of portionsof a gantry for a transport mechanism for use in CBCT X-ray imagingsystems. As shown in FIGS. 17A and 17B, the frame 174 of the gantry 36of the transport mechanism 170 can use a massive integrated structure towithstand the bending forces created and/or applied by the counterweight182, the detector 24 and/or the source 22. Further, the frame 174 caninclude first or top portion 174 a, second or lower portion 174 b thatextend toward or into the scan volume 228, which can be connected byframe connecting portion 174 c. In one embodiment, the portion 174 a,the portion 174 b, and the portion 174 c, can form an interior pocket174 d (see FIG. 12A) extending at least partially between the portion174 a and the portion 174 b. FIG. 17B shows an exterior surface of theframe 174 of the gantry 36. As shown in FIGS. 17A and 17B, the frame 174can be integrally formed, integrated affixed in sections, rigidlyconnected or the like.

In one embodiment, a detector can include a grid, which can be integralor removably attached. As shown in FIGS. 17A and 17B, in its positionagainst the detector 24 along the detector path, exemplary grid 242 isconstrained for six degrees of freedom (DOF). This is provided bythree-point constraint against detector 24, two-point constraint againststop 246, and a single point of constraint against bracket 244.

Certain exemplary embodiments of X-ray imaging systems (e.g., volumeradiographic imaging systems, CBCT systems) and/or methods for using thesame can provide a detector and a counterweight separately (e.g.,scanner or gantry) even though the counterweight and detector can bepositioned in or traverse the same relative space. In one embodiment,X-ray imaging systems and/or methods can provide a detector and acounterweight near distal ends of separate support arms (e.g., first andsecond support arms or a detector weight support unit with acounterweight support unit). In other embodiments, a detector andcounterweight can be coupled to a gantry mechanism or transportmechanism (e.g., of a scanner) and configured to move independently fromone another.

In certain exemplary embodiments, imaging systems (e.g., CBCT systems)can provide two separate supports individually for a detector and acounterweight. Further, separate supports structures can provide theability to position the detector relative to the source during scanningwith reduced or minimal movement or vibration. In certain exemplaryembodiments, a weaker, lighter, smaller, different material and/or moreflexible support for the counterweight can reduce the total weight ofmaterials from that used to position and support the detector and thecounterweight as a single unit. Further, separate supports can allowpositioning of the counterweight proximate the detector path whileallowing independent motion with increased vibration of thecounterweight during scanning that has reduced impact or minimal impacton the quality of the diagnostic radiographic imaging or imaging dataobtained. In addition, providing two separate supports individually fora detector and a counterweight can allow different materials (e.g., withdifferent characteristics such as but not limited to density, strength,rigidity, resistance to bending, cost or the like) to be used forrespective support structures for the detector and the counterweight.

FIGS. 18A-18D are diagrams that show an exemplary embodiment of acounterweight support mechanism for use with a gantry for a transportmechanism for use in radiographic imaging systems (e.g., CBCT X-rayimaging systems) and/or methods for using the same. As shown in FIGS.18A-18D, two separate supports can include a detector weight support arm310 coupled to support the detector 24 and a counterweight support arm320 (e.g., separate and individually provided) coupled to support acounterweight 382. In certain exemplary embodiments, the detector weightsupport arm 310 and the counterweight support arm 320 can be made fromdifferent materials or combinations of materials. As shown in FIGS.18A-18D, the detector weight support arm 310 and the counterweightsupport arm 320 can be coupled at first ends to a gantry 336 and atsecond (or distal) ends coupled to the detector 24 and the counterweight382, respectively. In certain exemplary embodiments, the detector weightsupport arm 310 and the counterweight support arm 320 are separated by afirst clearance gap 350 a. In one embodiment, the detector 24 and thecounterweight 382 can be separated by a second clearance gap 350 b.Preferably, the detector weight support arm 310 and the counterweightsupport arm 320 can extend circumferentially around without impingingthe scan volume. In one embodiment, the counterweight support arm 320can include a curved shape of a C-arm or other curved extensions betweenits mount to the gantry 336 and the counterweight 382. As shown in FIGS.18A-18D, the detector weight support arm 310 can be positioned inside(e.g., radially or relative to the scan volume) the counterweightsupport arm 320. Preferably, the source 22 is also mounted to the gantry336 (or other portion of a transport mechanism). In one embodiment, oneor more sources 22 and the detector 24 can be mounted in the gantry 336that is part of a transport assembly that can be controllably revolved(e.g., rotatable at least partially about a scan volume or axis β).

In certain exemplary embodiments, the counterweight support arm 320 canhave any prescribed 3D shape to attach the counterweight 382 to thescanner without crossing the scan volume 0.228. For example, thecounterweight support arm 320 can include the shape of a C-arm or anarcuate extension between a source mount at the gantry and thecounterweight. Alternatively, a counterweight support arm can include acurved or non-linear shape between a mount connection to the gantrymechanism and a mount connection to the counterweight. In otherembodiments, the counterweight support arm can include a series oflinear sections that together form a prescribed form between the gantrymechanism and the counterweight. Any configuration (e.g., mechanical orelectro-mechanical) is envisioned that locates the counterweight in theintended position physically separated from the detector, which ismounted to receive radiation from the source across an opening or scanvolume. In one embodiment, the detector weight support mechanism and thecounterweight support mechanism have similar (or identical) shapes. Inone embodiment, a detector weight support mechanism and a counterweightsupport mechanism have similar sickle shapes. In one embodiment, thedetector weight support mechanism or the counterweight support mechanismcan include a form that crosses below or above the scan volume. In oneembodiment, the detector weight support mechanism or the counterweightsupport mechanism can have similar shapes that encircle the scan volume.

In certain exemplary embodiments, the detector weight support arm 310 isconfigured to limit the detector 24 motion during scanning of the scanvolume 228 to less than ½, ⅕ or 1/10 of the motion of the counterweight382 allowed by the counterweight support arm 320 during scanning of thescan volume 228. In one embodiment, the detector weight support arm 310can connect the detector 24 to the source 22 (e.g., gantry 336) suchthat less than 5 mm, less than 3 mm or less than 1 mm of motion iscreated at the detector 24 (e.g., or relative motion between the source22 and the detector 24) during scanning of the scan volume 228. In oneembodiment, the counterweight support arm 320 connects the counterweight382 to the source 22 (e.g., gantry 336) such that less than 12 mm, lessthan 8, or less than 3 mm of motion is created at the counterweight 382during scanning of the scan volume 228. In one embodiment, the detectorweight support arm 310 can secure the detector 24 to a gantry mechanismwith reduced movement as compared to known configurations where thedetector and counterweight move and/or are mounted as a single unit(e.g., using frame 174).

In certain exemplary embodiments, providing two separate supportsindividually for a detector and a counterweight can provide the abilityto provide a prescribed size clearance gap between the detector and thecounterweight. In one embodiment, the clearance gap can be a preset3-dimensional gap, a 2-dimensional gap or a distance between thedetector weight support arm 310 and the counterweight support arm 320(or between the detector 24 and the counterweight 382). In oneembodiment, a clearance gap can be set responsive to (e.g.,proportional, weighted, non-linear) to the amount of calculated movement(e.g., deflection) and/or actual movement of the counterweight 382during scanning of the scan volume 228 or during any movement of a CBCTradiographic imaging system. In one embodiment, a clearance gap can beset responsive to (e.g., proportional, weighted, non-linear) to theamount of calculated movement (e.g., deflection) and/or actual movementof the detector 24 (source movement, relative movement between detectorand source, scanner, etc.) during scanning of the scan volume 228 orduring any movement of the CBCT radiographic imaging system.

In certain exemplary embodiments, providing two separate supportsindividually for the detector and the counterweight can provideincreased bore size and/or increased scan volume of a CBCT radiographicimaging system. In certain exemplary embodiments, providing two separatesupports individually for the detector 24 and the counterweight 382 canprovide the ability to increase a bore size and/or increase a scanvolume of a CBCT radiographic imaging system. Preferably, whilemaintaining or reducing calculated or actual movement between the source22 the detector 24 during scanning of the scan volume 228.

FIGS. 19A-19B are diagrams that show an exemplary embodiment of acounterweight support mechanism for use with a gantry for a transportmechanism for use in CBCT radiographic imaging systems or the like. Asshown in FIGS. 19A-19B, two separate supports can include a detectorweight support arm 410 coupled to support the detector 24 andcounterweight support arm 420 (e.g., separate and individually provided)coupled to support a counterweight 482. As shown in FIGS. 19A-19B, thedetector weight support arm 410 and the counterweight support arm 420can be coupled at first ends to a gantry and at second (or distal) endscoupled to the detector 24 and the counterweight 482, respectively. Incertain exemplary embodiments, the detector weight support arm 410 andthe counterweight support arm 420 are separated by a first clearance gap450 a. In one embodiment, the detector 24 and the counterweight 482 canbe separated by a second clearance gap 450 b. Preferably, the detectorweight support arm 410 and the counterweight support arm 420 can extendoutside or circumferentially around without impinging the scan volume.As shown in FIGS. 19A-19B, the detector weight support arm 410 can bepositioned inside (e.g., radially or relative to the scan volume) thecounterweight support arm 420 so that a paired extremity can passtherebetween. Preferably, the source 22 is also mounted to the gantry336.

FIGS. 20A-20B are diagrams that show an exemplary embodiment of acounterweight support mechanism for use with a gantry for a transportmechanism for use in CBCT radiographic imaging systems or the like. Asshown in FIGS. 20A-20B, two separate supports can include a detectorweight support arm coupled to support the detector 24 and counterweightsupport arm (e.g., separate and with multiple extensions) coupled tosupport a counterweight 482. As shown in FIGS. 20A-20B, a detectorweight support arm 510 and/or the counterweight support arm can beformed as a plurality of support arms/units (e.g., mechanically orelectro-mechanically connected or separated) coupled at one or morefirst ends to a gantry and at one or more second (or distal) endscoupled to the detector 24 and the counterweight 482, respectively.

In certain embodiments, a detector weight support arm and/or acounterweight support arm are shown as separate units that are attachedto the gantry 36 (or scanner 110). In alternative exemplary embodiments,detector weight support arm and/or a counterweight support arm can beintegrally formed as a single unit with one or more portions of atransport mechanism (e.g., gantry 36) or a scanner 110.

Radiographic imaging systems typically use a linear grid as ananti-scatter device that improves contrast and signal to noise (S/N)ratio in radiographic images. A grid typically includes a series of leadfoil strips that block x-rays separated by spacers that are transmissiveto x-rays. The spacing of the strips determines the grid frequency, andthe height-to-distance between lead strips determines a grid ratio.These and other grid characteristics can vary depending on the radiationenergy that is used for a particular image. Calibration of the detectortakes grid characteristics into account, so that different calibrationdata are used for different grids. In certain exemplary embodimentsherein, a detector can include a grid, which can be integral orremovably attached to the detector. Certain exemplary embodimentsaccording to the application can provide grid access (e.g., through door176) for replacement with a different grid or removal of the grid fromthe imaging path. In one embodiment, a detector does not include a grid.

Consistent with at least one embodiment, exemplary methods/apparatus canuse a computer program with stored instructions that perform on imagedata that is accessed from an electronic memory. As can be appreciatedby those skilled in the image processing arts, a computer program of anembodiment herein can be utilized by a suitable, general-purposecomputer system, such as a personal computer or workstation. However,many other types of computer systems can be used to execute the computerprogram of described exemplary embodiments, including an arrangement ofnetworked processors, for example.

The computer program for performing methods of certain exemplaryembodiments described herein may be stored in a computer readablestorage medium. This medium may comprise, for example; magnetic storagemedia such as a magnetic disk such as a hard drive or removable deviceor magnetic tape; optical storage media such as an optical disc, opticaltape, or machine readable optical encoding; solid state electronicstorage devices such as random access memory (RAM), or read only memory(ROM); or any other physical device or medium employed to store acomputer program. Computer programs for performing exemplary methods ofdescribed embodiments may also be stored on computer readable storagemedium that is connected to the image processor by way of the internetor other network or communication medium. Those skilled in the art willfurther readily recognize that the equivalent of such a computer programproduct may also be constructed in hardware.

It should be noted that the term “memory”, equivalent to“computer-accessible memory” in the context of the present disclosure,can refer to any type of temporary or more enduring data storageworkspace used for storing and operating upon image data and accessibleto a computer system, including a database, for example. The memorycould be non-volatile, using, for example, a long-term storage mediumsuch as magnetic or optical storage. Alternately, the memory could be ofa more volatile nature, using an electronic circuit, such asrandom-access memory (RAM) that is used as a temporary buffer orworkspace by a microprocessor or other control logic processor device.Display data, for example, is typically stored in a temporary storagebuffer that can be directly associated with a display device and isperiodically refreshed as needed in order to provide displayed data.This temporary storage buffer can also be considered to be a memory, asthe term is used in the present disclosure. Memory is also used as thedata workspace for executing and storing intermediate and final resultsof calculations and other processing. Computer-accessible memory can bevolatile, non-volatile, or a hybrid combination of volatile andnon-volatile types.

It will be understood that computer program products for exemplaryembodiments herein may make use of various image manipulation algorithmsand processes that are well known. It will be further understood thatexemplary computer program product embodiments herein may embodyalgorithms and processes not specifically shown or described herein thatare useful for implementation. Such algorithms and processes may includeconventional utilities that are within the ordinary skill of the imageprocessing arts. Additional aspects of such algorithms and systems, andhardware and/or software for producing and otherwise processing theimages or co-operating with the computer program product of theapplication, are not specifically shown or described herein and may beselected from such algorithms, systems, hardware, components andelements known in the art.

It should be noted that while the present description and examples areprimarily directed to radiographic medical imaging of a human or othersubject, embodiments of apparatus and methods of the present applicationcan also be applied to other radiographic imaging applications. Thisincludes applications such as non-destructive testing (NDT), for whichradiographic images may be obtained and provided with differentprocessing treatments in order to accentuate different features of theimaged subject.

Although sometimes described herein with respect to CBCT digitalradiography systems, embodiments of the application are not intended tobe so limited. For example, other DR imaging system such as dental DRimaging systems, mobile DR imaging systems or room-based DR imagingsystems can utilize method and apparatus embodiments according to theapplication. As described herein, an exemplary flat panel DRdetector/imager is capable of both single shot (radiographic) andcontinuous (fluoroscopic) image acquisition. Further, a fan beam CT DRimaging system can be used.

Exemplary DR detectors can be classified into the “direct conversiontype” one for directly converting the radiation to an electronic signaland the “indirect conversion type” one for converting the radiation tofluorescence to convert the fluorescence to an electronic signal. Anindirect conversion type radiographic detector generally includes ascintillator for receiving the radiation to generate fluorescence withthe strength in accordance with the amount of the radiation.

Exemplary embodiments according to the application can include variousfeatures described herein (individually or in combination). Priority isclaimed from commonly assigned, copending U.S. provisional patentapplication Ser. No. 61/710,832, filed Oct. 8, 2012, entitled “ExtremityScanner and Methods For Using The Same”, in the name of John Yorkston etal., the disclosure of which is incorporated by reference.

While the invention has been illustrated with respect to one or moreimplementations, alterations and/or modifications can be made to theillustrated examples without departing from the spirit and scope of theappended claims. In addition, while a particular feature of theinvention can have been disclosed with respect to one of severalimplementations, such feature can be combined with one or more otherfeatures of the other implementations as can be desired and advantageousfor any given or particular function. The term “at least one of” is usedto mean one or more of the listed items can be selected. The term“about” indicates that the value listed can be somewhat altered, as longas the alteration does not result in nonconformance of the process orstructure to the illustrated embodiment. Finally, “exemplary” indicatesthe description is used as an example, rather than implying that it isan ideal. Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

1. An imaging apparatus for cone beam computed tomography imaging, theapparatus comprising: a support structure that includes at least onesupport column; and a scanner that is coupled to the support column withat least three-dimensional movement, where the scanner comprises: a) agantry comprising: (i) a detector weight support arm configured tocouple a detector to the gantry for movement along a detector pathpartially around the scan volume to acquire image data according toreceived radiation; (ii) a radiation source that is energizable todirect radiation through the scan volume, wherein the radiation sourceis coupled to the gantry for movement along a source path partiallyaround the scan volume, where the source path is longer than thedetector path; and (iii) a counterweight support arm configured tocouple a counterweight to the gantry separate from the detector weightsupport arm.
 2. The imaging apparatus of claim 1, where the gantrycomprises a turntable and a mounting structure secured to rotate aroundthe turntable, the radiation source is attached to the mountingstructure, where the detector weight support arm is a C-shaped armmounted to the mounting structure.
 3. The imaging apparatus of claim 1,where the counterweight support arm is configured to provide independentmovement of the counterweight relative to the detector.
 4. The imagingapparatus of claim 1, where the counterweight support arm is configuredto provide a prescribed size clearance gap between the detector and thecounterweight.
 5. The imaging apparatus of claim 4, where the detectoron the detector weight support arm and the counterweight on thecounterweight support arm are separately provided with a gaptherebetween, and where the prescribed size clearance gap is responsiveto a movement amount of the counterweight.
 6. The imaging apparatus ofclaim 1, where relative motion of the counterweight during scanning ofthe scan volume is at least 5× greater than the motion of the detectorduring scanning of the scan volume.
 7. The imaging apparatus of claim 1,where the detector weight support arm and the counterweight support armare parallel to one another, where one of the detector weight supportarm and the counterweight support arm is closer to the scan volume,where the detector weight support arm and the counterweight support armare over one another in a direction along a longitudinal or radial axisof the scan volume, or where the detector weight support arm and thecounterweight support arm are separated back to a mounting point at thegantry.
 8. The imaging apparatus of claim 1, where the detector weightsupport arm and the counterweight support arm are different materials.9. The imaging apparatus of claim 1, where the detector is coupled neara distal end of the detector weight support arm and the counterweight iscoupled near a distal end of the counterweight support arm.
 10. Theimaging apparatus of claim 1, where the detector weight support arm andthe counterweight support arm being two separate supports respectivelyfor the detector and the counterweight operate to position the detectorrelative to the source during scanning with reduced movement orvibration.
 11. The imaging apparatus of claim 10, where the detectorweight support arm connects the detector to the source such that lessthan 10 mm of motion is created at the detector during scanning of thescan volume.
 12. The imaging apparatus of claim 1, where the detectorweight support arm is configured to limit detector motion duringscanning of the scan volume to less than 1/10 of the motion of thecounterweight allowed by the counterweight support arm during scanningof the scan volume.
 13. The imaging apparatus of claim 1, where thedetector weight support arm and the counterweight support arm being twoseparate supports respectively for the detector and the counterweightoperate to increase a scan volume of the CBCT radiographic imagingsystem.
 14. The imaging apparatus of claim 1, further comprising:scanner housing to provide a gap in the detector path and the sourcepath for radial access to the scan volume; and a door that moves intothe gap from a first position that does not obstruct the gap to a secondposition that extends into the gap.
 15. A method for cone beam computedtomography, the method comprising: moving a detector along at least aportion of a detector path, the at least a portion of the detector pathextending so that the detector is configured to move at least partiallyaround an imaging volume of the CBCT apparatus, the imaging volume ofthe CBCT apparatus to be positioned within the detector path;controllably moving a source along at least a portion of a source pathin coordination with the moving the detector along at least the portionof the detector path, the at least a portion of the source pathextending so that the source is configured to move at least partiallyaround the imaging volume of the CBCT apparatus, the imaging volume ofthe CBCT apparatus to be positioned within the source path, the sourcepath being sufficiently long to allow adequate radiation exposure of theimaging volume of the CBCT apparatus for an image capture by thedetector; and controllably moving a counterweight proximate to said atleast the portion of the detector path separate from the detector. 16.The method of claim 15, where a detector weight support arm isconfigured to move the detector along the portion of the detector path,where a counterweight support arm is configured to move thecounterweight proximate to the portion of the detector path.
 17. Animaging apparatus for cone beam computed tomography imaging, theapparatus comprising: a radiation source arranged on one side of animaging volume to generate an electromagnetic beam; a radiation detectorarranged on an opposite side of the imaging volume from said radiationsource, said radiation detector being structured and arranged to receivesaid electromagnetic beam; means for revolving said radiation source andsaid radiation detector substantially around the imaging volume in acontrolled manner whereby a tomographic effect is produced; first meansfor connecting said radiation source to the means for revolving; secondmeans for connecting said radiation detector to the means for revolving;and third means for connecting a counterweight to the means forrevolving independently from said second means for connecting.